Process for producing sintered color pencil lead

ABSTRACT

Disclosed is a process for producing a sintered color pencil lead characterized by pigmenting a white or light-colored porous sintered pencil lead with an organic pigment by treating said porous sintered pencil lead with a solution of at least one compound of the following Formula (I) to be filled with said compound and then by forming said organic pigment within the pores by means of heating, 
     
       
         A(B)x 
       
     
     in which x is an integer from 1 to 8, 
     A is the radical of a chromophore of the quinacridone, anthraquinone, perylene, indigo, quinophthalone, indanthrone, isoindolinone, isoindoline, dioxazine, azo series, phthalocyanine or diketopyrrolopyrrole which is attached to x groups B via one or more heteroatoms selected from the group consisting of N, O and S and forming part of the radical A, 
     B is hydrogen or a group of the formula                    
     where at least one group B is not hydrogen and, if x is 2 to 8, all the groups B can be identical or different, and L is any suitable solubilizing group.

TECHNICAL FIELD

The present invention relates to a process for producing a sinteredcolor pencil lead which can draw lines having excellent light fastnessand weatherability while having a vivid coloring property and asufficiently high density in drawn lines and is excellent in amechanical strength such as a bending strength and which can readily beerased with an eraser and is particularly suited as a fine size colorpencil lead for a mechanical pencil.

BACKGROUND ART

Conventional sintered color pencil leads are used for mechanical pencilsin many cases, and a production process therefor includes a principalproduction process in which a blend composition comprising an fillersuch as boron nitride and a binder such as clay is kneaded, extruded andthen subjected to heat treatment to prepare a porous lead and in whichan ink comprising a dye is filled into pores of this lead.

However, since the colorant is a dye, the problem with the dye is thatthe stability with the passage of time such as light fastness isinferior. Further, if a lead has pores having a size at the level inwhich the pores can be impregnated with a pigment-dispersed ink, thelead is weak in strength and can not serve as a practical lead for amechanical pencil.

The present applicant has heretofore filed Japanese Patent ApplicationLaid-Open No. Hei 8-48931, Japanese Patent Application Laid-Open No. Hei9-67540, Japanese Patent Application Laid-Open No. Hei 2000-17220 andJapanese Patent Application Laid-Open No. Hei 2000-17221 in connectionwith methods for obtaining a lead having a high strength. In all ofthese methods, obtained are sintered leads which can be impregnated witha pigment-dispersed ink so as to provide drawn lines with a high densityand which is stronger in strength than the practical level applicable toa lead for a mechanical pencil. However, further desired is a sinteredlead whose density in drawn lines thereof is further more improved andwhose strength is further more than the practical level.

Further, the present inventors have filed Japanese Patent ApplicationLaid-Open No. Hei 8-143810, Japanese Patent Application Laid-Open No.Hei 8-143811, Japanese Patent Application Laid-Open No. Hei 8-143812 andJapanese Patent Application Laid-Open No. Hei 8-259874 in connectionwith methods for producing organic pigments in pores of a porous leadfor a mechanical pencil by chemical reaction. These methods have made itpossible to impregnate pores of a lead having a small pore diameter withan organic pigment. However, problems with these methods are that, sincethe reaction is carried out in the presence of a strong acid or a strongbase, the leads are liable to be a little deteriorated and that, sincethe production process is different according to each pigment, mixingcolor and producing multiple color are difficult.

DISCLOSURE OF THE INVENTION

An object of the present invention is to solve the defects of thesintered color pencil leads produced by the conventional techniquesdescribed above and further improve the prior art of the presentinventors described above and to provide a process for producing asintered color pencil lead which can draw lines having excellent lightfastness and weatherability while having a vivid coloring property and asufficiently high density in drawn lines and is excellent in amechanical strength such as a bending strength and which can readily beerased with an eraser.

The present inventors have done intensive researches in order to solvethe problems described above. As a result, they have found that theabove problems can be solved by filling pores of a white orlight-colored porous sintered lead with a specific compound andpigmenting the compound by heating, and thus they have come to completethe present invention.

That is, a process for producing a sintered color pencil leadcharacterized by forming a white or light-colored porous sintered pencillead that is pigmented with an organic pigment by treating said poroussintered pencil lead with a solution of at least one compound of thefollowing Formula (I) to be filled with said compound and then byforming said organic pigment within the pores by means of heating,

A(B)x  (I)

in which x is an integer from 1 to 8,

A is the radical of a chromophore of the quinacridone, anthraquinone,perylene, indigo, quinophthalone, indanthrone, isoindolinone,isoindoline, dioxazine, azo series, phthalocyanine ordiketopyrrolopyrrole which is attached to x groups B via one or moreheteroatoms selected from the group consisting of N, O and S and formingpart of the radical A,

B is hydrogen or a group of the formula

where at least one group B is not hydrogen and, if x is 2 to 8, all thegroups B can be identical or different, and L is any suitablesolubilizing group.

To be more specific, pores of a white or light-colored porous sinteredlead comprising a colorless or white filler and silicon nitride preparedfrom a starting material of perhydropolysilazane which is a binder maybe filled with a solution prepared by dissolving the compound (I)described above in an organic solvent and pigmented by heating.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment of the present invention shall be explained below indetail.

A process for producing a sintered color pencil lead characterized byforming a white or light-colored porous sintered pencil lead that ispigmented with an organic pigment by treating said porous sinteredpencil lead with a solution of at least one compound of the followingFormula (I) to be filled with said compound and then by forming saidorganic pigment within the pores by means of heating,

A(B)x  (I)

in which x is an integer from 1 to 8,

A is the radical of a chromophore of the quinacridone, anthraquinone,perylene, indigo, quinophthalone, indanthrone, isoindolinone,isoindoline, dioxazine, azo series, phthalocyanine ordiketopyrrolopyrrole which is attached to x groups B via one or moreheteroatoms selected from the group consisting of N, O and S and formingpart of the radical A,

B is hydrogen or a group of the formula

where at least one group B is not hydrogen and, if x is 2 to 8, all thegroups B can be identical or different, and L is any suitablesolubilizing group.

In a process for producing a sintered color pencil lead in accordancewith the present invention, a white or light-colored porous sinteredlead is formed and pores of the white or light-colored porous sinteredlead are filled with a solution prepared by dissolving at least thecompound (I) described above in an organic solvent and pigmented saidcompound in said pores by heating.

In the present invention, the porous sintered lead is formed from acolorless or white filler which is a publicly known substance, such asboron nitride, talc and mica and a binder such as silicon nitride,silica, alumina and zirconia and a solid solution thereof or clay. Inparticular, preferably suitable in terms of strength is a leadcomprising a binder of silicon nitride prepared fromperhydropolysilazane used as a starting material, which is disclosed inJapanese Patent Application Laid-Open No. Hei 8-48931.

The filler shall not specifically be restricted as long as it hasheretofore been used as an filler for a sintered color pencil lead andis colorless or white, and any substances can be used. For example, thefiller described above can be used, and it is a matter of course that amixture of several kinds thereof can be used. Further, silica andalumina can be used as the filler depending on the kind and thesintering temperature of the binder.

A pore diameter of the porous color pencil lead used in the presentinvention shall not specifically be restricted as long as it can beimpregnated with a solution prepared by dissolving the compound ofFormula (I) in an organic solvent. However, a minimum value of the porediameter is considered to be about 0.1 μm, so that it is preferable touse those in which all pore diameters are 0.1 μm or more. Taking adistribution of the pores into consideration, if the pores having adiameter falling in a range of smaller than 0.1 μm are distributed in alarge number, then the pores which can not be filled with a pigmentincrease to deteriorate the coloring property, and therefore it ispreferable that the pores having a diameter of smaller than 0.1 μmaccount for 40% or less, more preferable 20% or less based on the totalvolume.

Considering strength of the lead, the pore diameter has preferably amaximum value of 0.4 μm or less.

Considering the coloring property onto a paper surface, the porositydistributing in a range of 0.1 μm or more and 0.4 μm or less, preferably0.1 μm or more and 0.3 μm or less in the pore diameter of the porouspencil lead accounts for preferably 10 vol % or more, more preferably 15vol % or more based on a volume of the lead.

In the present invention, the sintered color pencil lead is obtained byimpregnating and filling the pores of the sintered lead described abovewith the compound of Formula (I) dissolved in an organic solvent andthen heating the lead to convert the compound into an organic pigment.

The group A of the Formula (I) is a publicly known chromophore having abasic structure:

A(H)_(x)

for example, a residue of compounds described below and all publiclyknown derivatives thereof. Classification of the following compounds byitem is not based on chemical classification.

In the present invention, the groups of the preferred compounds ofFormula (I) shall be shown in the following a) to l).

a) Perylencarboximides of the following formulae:

in which D is C₁-C₆alkyl, unsubstituted or halo- orC₁-C₆alkyl-substituted phenyl, benzyl or phenethyl or B, where B isidentical to that described above.

b) Quinacridones of the following formula (III):

in which R₁ and R₂ independently of one another are hydrogen, halogen,C₁-C₂₄alkyl, C₁-C₆alkoxy or phenyl, and E is hydrogen or a group of thefollowing formula:

in which L is any suitable solubilizing group, with the proviso that atleast one of the groups E is a group other than hydrogen.

c) Dioxazines of the following formulae:

in which R₃ is hydrogen, halogen or C₁-C₂₄alkyl, and E is identical tothat described above,

in which R₄, R₅ and R₆ independently of one another are hydrogen,C₁-C₄alkyl, C₁-C₄alkoxy, NECO—C₁-C₄alkyl, NECO-phenyl or N(E)₂, where atleast one of R₄, R₅ and R₆ is NECO—C₁-C₄alkyl, NECO-phenyl or N(E)₂, andE is identical to that described above.

d) Isoindolines of the following formulae:

in which R₇ is a group:

R₈ is hydrogen, C₁-C₂₄alkyl, benzyl or

a group:

R₉ is hydrogen, E or R₇,

R₁₀, R₁₁, R₁₂ and R₁₃ independently of one another are hydrogen,

C₁-C₂₄alkyl, C₁-C₆alkoxy, halogen or trifluoromethyl, and E is identicalto that described above.

e) Isoindolinones of the following formulae:

in which R₁₄ and R₁₅ independently of one another are hydrogen, halogenor C₁-C₄alkyl, and E is identical to that described above.

f) Anthraquinoid compounds of the following formulae:

in which R₁₆'s independently of one another are hydrogen or halogen, andE is identical to that described above.

g) Phthalocyanine of the following formula:

in which M is H₂, a divalent metal selected from the group consisting ofCu (II), Zn (II), Fe (II), Ni (II), Ru (II), Rh (II), Pd (II), Pt (II),Mn (II), Mg (II), Be (II), Ca (II), Ba (II), Cd (II), Hg (II), Sn (II),Co (II) and Pb (II), (preferably a divalent metal selected from thegroup consisting of Cu (II), Zn (II), Fe (II), Ni (II) and Pd (II)), ora divalent metal oxide selected from the group consisting of V(O), Mn(O)and TiO;

T₁ is —CHR₁₈—, —CO— or SO₂—;

R₁₇ is hydrogen, C₁-C₆alkyl, —N(E)R₁₈, N(E)₂, —NECOR₁₉, —COR₁₉ or agroup;

R₁₈ is hydrogen or C₁-C₆alkyl;

R₁₉ is C₁-C₆alkyl;

R₂₀ is hydrogen, halogen, C₁-C₆alkyl or C₁-C₆alkoxy;

Z is zero or 1;

y is an integer of 1 to 8, and E is identical to that described above.

h) Pyrrolo[3,4-c]pyrroles of the following formulae:

in which G₁ and G₂ independently of one another are any of the followinggroups, and E is identical to that described above.

in which R₂₁ and R₂₂ independently of one another are hydrogen, halogen,C₁-C₂₄alkyl, C₁-C₆alkoxy, C₁-C₁₈alkylmercapto, C₁-C₁₈alkylamino, —CN,—NO₂, phenyl, trifluoromethyl, C₅-C₆cycloalkyl, —C═N—(C₁-C₂₄alkyl),

a group;

imidazolyl, pyrazolyl, triazolyl, piperadinyl, pyrrolyl, oxazolyl,benzoxazolyl, benzothiazolyl, benzoimidazolyl, morpholinyl, piperidinylor pyrrolidinyl;

T₂ is —CH₂—, —CH(CH₃)—, —CH(CH₃)₂—, —CH═N—, —N═N—, —O—, —S—, —SO—, —SO₂—or —NR₂₇;

R₂₃ and R₂₄ independently of one another are hydrogen, halogen,C₁-C₆alkyl, C₁-C₆alkoxy or —CN;

R₂₅ and R₂₆ independently of one another are hydrogen, halogen orC₁-C₆alkyl;

R₂₇ is hydrogen or C₁-C₆alkyl.

i) Quinophthalones of the following formulae:

in which R₂₈ is hydrogen or O—E;

R₂₉, R₃₀, R₃₁, and R₃₂ independently of one another are hydrogen,halogen, —COO—C₁-C₆alkyl or —CONE—C₁-C₆alkyl; and E is identical to thatdescribed above.

j) Azo compounds of the following formulae:

in which R₃₃, R₃₄, R₃₅, R₃₆ and R₃₇ independently of one another arehydrogen, halogen, C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, acetyl or—SO₂NE—C₁-C₆alkyl;

R₃₈ is hydrogen, halogen, C₁-C₆alkyl or C₁-C₆alkoxy; and E is identicalto that described above.

k) Anthraquinones of the following formulae:

in which R₃₉ and R₄₀ independently of one another are hydrogen,C₁-C₁₂alkyl or C₆-C₁₂aryl which is unsubstituted or substituted byhalogen, C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, acetyl, SO₂NE—C₁-C₆alkyl or—SO₂NE₂;

R₄₁ and R₄₂ independently of one another are hydrogen, halogen,C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, cyano, CONE₂, SO₂NE—C₁-C₆alkyl or SO₂NE₂,SO₃E, SO₃Na or C₆-C₁₂aryl which is unsubstituted or substituted byhalogen, C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, acetyl, SO₂NE—C₁-C₆alkyl orSO₂NE₂;

R₄₃ is hydrogen, halogen, NO₂, cyano, hydroxyl or C₁-C₆alkoxy; and B andE are identical to that described above.

l) Indigo derivatives of the following formula:

in which R₄₄ is hydrogen, halogen, CN, C₁-C₆alkyl or C₁-C₆alkoxy, and Eis identical to that described above.

To describe in further details, preferred quinacridones are those,wherein in Formula (III) R₁ and R₂ independently of one another arehydrogen, chlorine or methyl.

Preferred pyrrolo[3,4-c]pyrroles are those, wherein in Formula XIII G₁and G₂ are identical and are a group of the following formulae:

wherein R₂₁ and R₂₂ independently of one another are hydrogen, chlorine,bromine, C₁-C₄alkyl, C₁-C₆alkoxy, C₁-C₁₆alkylamino, —CN or phenyl;

T₂ is —N═N—, —O—, —SO₂— or —NR₂₇; and

R₂₇ is hydrogen, methyl or ethyl.

Preferred azo compounds are those, wherein in Formulae (XVa) to (XVf)R₃₃, R₃₄, R₃₅, R₃₆ and R₃₇ independently of one another are hydrogen,halogen, methyl, methoxy, NO₂, acetyl or SO₂NECH₃ and R₃₈ is halogen ormethoxy.

In the present invention, particularly preferred is any one of thequinacridones of the following formulae:

wherein E is identical to that described above.

In the present invention, particularly preferred dioxazines are those ofthe following formula:

in which R₄₅ and R₄₆ independently of one another are C₁-C₄alkyl, and Eis identical to that described above.

In the present invention, particularly preferred pyrrolopyrroles arethose of the following formula:

in which R₄₇ and R₄₈ independently of one another are hydrogen, methyl,tert-butyl, chlorine, bromine, cyano or phenyl, and E is identical tothat described above.

In the present invention, particularly preferred phthalocyanines arethose of the Formula (XII) in which M is Cu (II) and R₁₆ is hydrogen orE, and z is 1 and y is 1 to 4 (E is identical to that described above).

In the present invention, particularly preferred isoindolines are thoseof the following formula:

in which R₄₉ is C₁-C₄alkyl, and E is identical to that described above.

In the present invention, particularly preferable indanthrones are thoseof the following formula:

in which E is identical to that described above.

In the present invention, particularly preferable azo compounds arethose, wherein in Formula (XVa), (XVb), (XVe) or (XVf) described above,R₃₃, R₃₄, R₃₅, R₃₆ and R₃₇ independently of one another are hydrogen,chlorine, methoxy, NO₂, acetyl or SO₂NECH₃, and R₃₈ is halogen ormethoxy (where E is identical to that described above).

In the present invention, particularly noteworthy soluble chromophoresare those which can be prepared from, for example, the following C. I.Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 83, Pigment Yellow109, Pigment Yellow 139, Pigment Orange 71, Pigment Orange 73, PigmentRed 122, Pigment Red 185, Pigment Red 202, Pigment Red 254, Pigment Red255, Pigment Red 264, Pigment Blue 25, Pigment Blue 26, Pigment Blue 60,Pigment Blue 64, Pigment Violet 19, Pigment Violet 29 and Pigment Violet37.

The compounds of Formulas (I) to (XXI) and the production processesthereof have already been publicly known and are disclosed in, forexample, EP648770, EP648817 and EP742556.

In accordance with the present invention, the preferred groups of thesolubilizing group —L in Formula (I) shall be shown below:

in which R₅₀, R₅₁ and R₅₂ independently of one another are C₁-C₆alkyl;

R₅₃ and R₅₄ independently of one another are C₁-C₆alkyl, O, S orN(R₆₁)₂-interrupted C₁-C₆alkyl, unsubstituted or halo-, C₁-C₆alkyl-,C₁-C₆alkoxy-, NO₂— or cyano-substituted phenyl or biphenylyl;

R₅₅, R₅₆ and R₅₇ independently of one another are hydrogen orC₁-C₆alkyl;

R₅₈ is hydrogen, C₁-C₆alkyl or any of the following groups:

R₅₉ and R₆₀ independently of one another are hydrogen, halogen,C₁-C₆alkyl, C₁-C₆alkoxy, cyano, NO₂, N(R₆₁)₂, unsubstituted or halo-,C₁-C₆alkyl-, C₁-C₆alkoxy-, NO₂— or cyano-substituted phenyl;

R₆₁ and R₆₂ are C₁-C₆alkyl;

R₆₃ is hydrogen or C₁-C₆alkyl;

R₆₄ is hydrogen, C₁-C₆alkyl, unsubstituted or C₁-C₆alkyl-substitutedphenyl;

Q is p,q-C₂-C₆alkylene which is unsubstituted or substituted once ormore times by C₁-C₆alkoxy, C₁-C₆alkylmercapto or C₂-C₁₂dialkylamino(where p and q are different numeric locants);

X is a heteroatom selected from the group consisting of N, O and S,where m is 0 if X is O or S and is 1 if X is N;

L₁ and L₂ independently of one another are unsubutituted or mono- orpoly-C₁-C₁₂alkoxy, —C₁-C₁₂alkylmercapto, —C₂-C₂₄dialkylamino,—C₆-C₁₂aryloxy, —C₆-C₁₂arylmercapto, —C₇-C₂₄alkylarylamino or—C₁₂-C₂₄diarylamino-substituted C₁-C₆alkyl, or[-(p′,q′-C₂-C₆alkylene)-Z—]_(n)—C₁-C₆alkyl (where n is a number of 1 to1000; p′ and q′ are different numeric locants; each Z independently ofthe others is a heteroatom comprising oxygen, sulfur orC₁-C₁₂alkyl-substituted nitrogen; and all C₂-C₆alkylenes in therepeating units [—C₂-C₆alkylene-Z—] can be identical or different);

L₁ and L₂ can be saturated or mono- to deca-unsaturated, uninterruptedor interrupted in any desired points by from 1 to 10 groups selectedfrom the group consisting of —(C═O)— and —C₆H₄—, and may carry no or 1to 10 further substituents selected from the group halogen, cyano andNO₂.

Preferable are compounds of Formula (I) in which L is C₁-C₆alkyl or agroup:

in which Q is C₂-C₄alkylene, and L₁ and L₂ are[—C₂-C₁₂alkylene-Z—]_(n)—C₁-C₁₂alkyl or C₁-C₁₂alkyl which is substitutedonce or more times by C₁-C₁₂alkoxy, C₁-C₁₂alkylmercapto orC₂-C₂₄dialkylamino (m and n are as defined above).

Further preferable are compounds of Formula (I) in which L is C₄-C₅alkylor the group of the following formula:

in which Q is C₂-C₄alkylene, X is oxygen (in this case, m is 0), and L₂is [—C₂-C₁₂alkylene-O—]_(n)—C₁-C₁₂alkyl or C₁-C₁₂alkyl which issubstituted once or more times by C₁-C₁₂alkoxy, especially those inwhich —Q—X— is —C(CH₃)₂—CH₂—O—.

Further more preferable pigment precursors of the present invention arecompounds of Formula (I) in which the group L is tert-butyl ortert-amyl.

Alkyl and alkylene can be straight-chain, branched, monocyclic andpolycyclic.

Specific examples of C₁-C₁₂alkyl include methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, cyclobutyl,n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, cyclopentyl,cyclohexyl, n-hexyl, n-octyl, 1,1,3,3-tetramethylbutyl, 2-ethylhexyl,nonyl, trimethylcyclohexyl, decyl, menthyl, thujyl, bornyl, 1-adamantyl,2-adamantyl and dodecyl.

Further, if C₂-C₁₂alkyl is an unsaturated compound having two or moredouble bonds such as C₂-C₁₂alkenyl, C₂-C₁₂alkynyl, C₂-C₁₂alkapolyenyland C₂-C₁₂alkapolyinyl, specific examples of this C₁-C₁₂alkyl are vinyl,allyl, 2-propene-yl, 2-butene-1-yl, 3-butene-1-yl, 1,3-butadiene-2-yl,2-cyclobutene-1-yl, 2-pentene-1-yl, 3-pentene-2-yl,2-methyl-1-butene-3-yl, 2-methyl-3-butene-2-yl, 3-methyl-2-butene-1-yl,1,4-pentadiene-3-yl, 2-cyclopentene-1-yl, 2-cyclohexene-1-yl,3-cyclohexene-1-yl, 2,4-cyclohexadiene-1-yl, 1-p-menthene-8-yl,4(10)-thujen-10-yl, 2-norbornene-1-yl, 2,5-norbornadiene-1-yl,7,7-dimethyl-2,4-norcaradiene, and various isomers such as hexynyl,octenyl, nonenyl, decenyl and dodecenyl.

Specific examples of C₂-C₄alkylene are 1,2-ethylene, 1,2-propylene,1,3-propylene, 1,2-butylene, 1,3-butylene, 2,3-butylene, 1,4-butyleneand 2-methyl-1,2-propylene.

Specific examples of C₅-C₁₂alkylene are various isomers of pentylene,hexylene, octylene, decylene and dodecylene.

C₁-C₁₂alkoxy is O—C₁-C₁₂alkyl, preferably O—C₁-C₄alkyl.

C₆-C₁₂ aryloxy is O—C₆-C₁₂aryl, and specific examples thereof arephenoxy or naphthoxy, preferably phenoxy.

C₆-C₁₂ arylmercapto is S—C₁-C₁₂aryl, and specific examples thereof arephenylmercapto and naphthylmercapto, preferably phenylmercapto.

C₂-C₂₄dialkylamino is N(alkyl₁)(alkyl₂), where the sum of the carbonatoms in the two groups alkyl₁ and alkyl₂ is from 2 to 24, preferablyN(C₁-C₄alkyl)-C₁-C₄alkyl.

C₇-C₂₄alkylarylamino is N(alkyl₁)(aryl₂), where the sum of the carbonatoms in the two groups alkyl₁ and aryl₂ is from 7 to 24, for examplemethylphenylamino, ethylnaphthylamino or butylphenanthrylamino,preferably methylphenylamino or ethylphenylamino.

C₁₂-C₂₄diarylamino is N(aryl₁)(aryl₂), where the sum of the carbon atomsin the two groups aryl₁ and aryl₂ is from 12 to 24, for examplediphenylamino or phenylnaphthylamino, preferably diphenylamino.

Halogen is chlorine, bromine, fluorine or iodine, preferably fluorine orchlorine.

n is preferably a number from 1 to 100, with particular preference anumber from 2 to 12.

Used as the organic solvent of the present invention are all ofaliphatic hydrocarbons, aromatic hydrocarbons, alcohols, amides,nitrites, nitro compounds, N-heterocyclic compounds, ethers, ketones andesters as long as they are publicly known and available in the marketand can dissolve the compounds of Formula (I) described above. Water canbe used as well if appropiate. These solvents have preferably a boilingpoint of 40 to 300° C.

To describe the solubility, the solvents which can dissolve the compound(I) in a proportion of 5% by weight or more, preferably 10% by weight ormore are preferred in terms of a density in drawn lines of the lead.Specific examples thereof are methanol, ethanol, isopropanol, n-butanol,benzyl alcohol, diethyl ether, 1-acetoxy-2-ethoxyethanol, acetone,methyl ethyl ketone, cyclopentanone, butyrolactone,1-methoxy-2-propanol, 1,2-dimethoxyethane, 1,2-diethoxyethane,2-methoxyethanol, 2-methoxy-propyl acetate, ethyl acetate, butylacetate, isopropyl laurate, methyl methacrylate, tetrahydrofuran,dioxane, acetonitrile, benzonitrile, nitrobenzene,N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide,N-methylpyrrolidone, pyridine, picoline, quinoline, dichloromethane,chloroform, methylcyclohexane, benzene, toluene, xylene,diisopropylnaphthalene, anisole and chlorobenzene. It is a matter ofcourse that these solvents can be used in a mixture thereof.

In the present invention, a method for filling a porous sintered leadwith a solution of the compound which is the pigment precursor ofFormula (I) described above comprises dipping the porous sintered leadinto the solution described above to fill the pores thereof with thesolution, if necessary, under conditions of heating and applyingpressure or reducing pressure.

Then, the organic solvent is removed by drying, and the lead is heatedat a temperature of 100 to 250° C., preferably 150 to 200° C. andparticularly preferably 160 to 200° C. which is optimum to therespective pigment precursors to convert the compound of Formula (I)described above into an organic pigment.

A catalyst such as, for example, an acid can be used if appropiate inorder to lower the pigmenting temperature.

Heating time for pigmenting is different according to the heatingtemperature, a size and a shape of the lead pores and other conditions,and therefore it can not generally be defined. It is approximatelyseveral seconds to several hours, preferably 1 to 30 minutes.

Further, dipping and heating may be repeated in order to increase adensity in the drawn lines.

The compounds which are the pigment precursors of Formula (I) can bemixed and dissolved in a solvent and heated to obtain an optional mixedcolor.

The lead obtained after the compound of Formula (I) described above isconverted into a pigment can be impregnated, if necessary, with alubricant such as oil, a UV absorber, a light stabilizer and anantistatic agent for the purpose of elevating stability with the passageof time and a writing feeling.

In the process for producing a sintered color pencil lead of the presentinvention thus constituted, the following effects (1) to (3) areprovided.

(1) The compound of Formula (I) described above can be dissolved in anorganic solvent in a high concentration, and a solution thereof has alow viscosity, so that a lead having such a small pore diameter as inthe present invention can be impregnated with said solution equally toor more than a dye ink. Accordingly, the pores of the lead can readilybe filled with the pigment in an amount sufficient for obtaining a highdensity in the drawn lines. Further, it is a solution of an organicsolvent, and therefore it does not deteriorate the lead comprisingceramics, clay and the like.

(2) A plurality of the compounds of Formula (I) described above can beblended in an optional proportion and dissolved in a specific organicsolvent, and multicoloring of the lead can easily be achieved. Further,the organic pigment obtained after heating the compound described aboveis stable with the passage of time, and therefore the sintered colorpencil lead which has a vivid coloring property and a sufficiently highdensity in the drawn lines and which is excellent in stability with thepassage of time such as light fastness can be obtained according to thepresent invention.

(3) The colorant for the sintered color pencil lead of the presentinvention is a solid pigment at the final stage and is not adhered ontoa paper face unlike the conventional dye inks, and therefore the colorpencil lead having an excellent erasability with an eraser is obtained.

EXAMPLES

Next, the present invention shall more specifically be explained withreference to examples and comparative examples, but the presentinvention shall by no means be restricted by the following examples.

Example 1

Boron nitride 40% by weight Vinyl chloride resin 43% by weight Dioctylphthalate (DOP) 16% by weight Oleic amide  1% by weight

The blend composition described above was mixed and dispersed by meansof a Henschel mixer and kneaded by means of a pressure kneader and a tworoll mill. Then, it was extruded into fine lines, and they weresubjected to heat treatment at 180° C. for 10 hours in the air in orderto remove the residual plasticizer and then heated up to 1000° C. in anitrogen atmosphere, followed by sintering at 1000° C. for one hour,whereby a first sintered lead was obtained.

This first sintered lead was sintered by heating at 700° C. in the airto remove carbons, whereby a white second sintered lead was obtained.

This second sintered lead 100 g was dipped into a vessel containing 140g of a xylene solution (20% by weight) of perhydropolysilazane and thenheated up to 1200° C. in a nitrogen atmosphere, followed by sintering at1200° C. for one hour, whereby a white third sintered lead having adiameter of 0.57 mm was obtained.

Next, the third sintered lead described above was dipped into an ethylacetate solution (20% by weight) of a pigment precursor No. 1 shown inthe following Table 1 and left standing at room temperature for 24hours.

The lead was taken out of the solution and then heated at 180° C. for 20minutes to obtain a yellow sintered pencil lead having a diameter of0.57 mm.

Example 2

A toluene solution (15% by weight) of a pigment precursor No. 2 shown inthe following Table 1 was used to dip thereinto the third sintered leadin the same manner as in Example 1, and the lead was left standing atroom temperature for 24 hours. The lead was taken out of the solutionand then heated at 180° C. for 20 minutes to obtain a red sinteredpencil lead having a diameter of 0.57 mm.

Example 3

A cyclopentanone solution (15% by weight) of a pigment precursor No. 3shown in the following Table 1 was used to dip thereinto the thirdsintered lead in the same manner as in Example 1, and the lead was leftstanding at room temperature for 24 hours. The lead was taken out of thesolution and then heated at 180° C. for 20 minutes to obtain a reddishpurple sintered pencil lead having a diameter of 0.57 mm.

Example 4

A tetrahydrofuran solution (15% by weight) of a pigment precursor No. 4shown in the following Table 1 was used to dip thereinto the thirdsintered lead in the same manner as in Example 1, and the lead was leftstanding at room temperature for 24 hours. The lead was taken out of thesolution and then heated at 180° C. for 20 minutes to obtain a lightblue sintered pencil lead having a diameter of 0.57 mm.

Example 5

100 g of the same second sintered lead as in Example 1 was dipped into avessel containing 140 g of a xylene solution (20% by weight) ofperhydropolysilazane and then heated up to 1200° C. in the air, followedby sintering at 1200° C. for one hour, whereby a third sintered leadhaving a diameter of 0.57 mm was obtained.

Next, the third sintered lead described above was dipped into a toluenesolution (20% by weight) of the pigment precursor No. 1 shown in thefollowing Table 1 and left standing at room temperature for 24 hours.The lead was taken out of the solution and then heated at 180° C. for 20minutes to obtain a yellow sintered pencil lead having a diameter of0.57 mm.

Example 6

Blend Composition A

Zirconium acetylacetonate.ethyl

acetoacetate 30.00% by weight Water  1.75% by weight Hydrochloric acid(36%)  0.45% by weight n-Butyl alcohol 44.30% by weight

The blend composition A described above was heated at 35° C. for onehour.

Blend Composition B

Boron nitride 13.00% by weight  Polyvinylbutyral 6.60% by weightTetraethylene glycol 3.90% by weight

The blend composition A which finished refluxing was added to the blendcomposition B described above, and they were mixed and dispersed bymeans of a mixer and kneaded by means of a two roll mill to adjust theamount of the solvent. Then, it was extruded into fine lines, and theywere dried at 200° C. in the air in order to remove the residual solventand plasticizer and then heated up to 1700° C. in an argon atmosphere,followed by being sintered at 1700° C. for one hour. Further, they wereheated up to 700° C. in the air and sintered at 700° C. for 3 hours toobtain a white sintered lead having a diameter of 0.57 mm.

Next, the sintered lead described above was dipped into atetrahydrofuran solution (20% by weight) of the pigment precursor No. 3shown in the following Table 1, and the lead was left standing at roomtemperature for 24 hours. The lead was taken out of the solution andthen heated at 180° C. for 20 minutes to obtain a reddish purplesintered pencil lead having a diameter of 0.57 mm.

Example 7

Boron nitride 40% by weight Kaolin 35% by weight Polyvinyl alcohol 18%by weight Polyethylene glycol  7% by weight

The blend composition described above was mixed with the same amount ofwater and dispersed by means of a Henschel mixer and kneaded by means ofa two roll mill to adjust the water content. Then, it was extruded intofine lines, and they were subjected to heat treatment at 105° C. for 15hours in the air in order to remove the residual water. Then, they wereheated up to 1100° C. in argon gas and sintered at 1100° C. for onehour. Further, they were heated and sintered at 700° C. in the air toremove carbons, whereby a white sintered pencil lead having a diameterof 0.57 mm was obtained.

Next, the sintered lead described above was dipped into a toluenesolution (15% by weight) of the pigment precursor No. 2 shown in thefollowing Table 1, and the lead was left standing at room temperaturefor 24 hours. The lead was taken out of the solution and then heated at180° C. for 20 minutes to obtain a red sintered pencil lead having adiameter of 0.57 mm.

TABLE 1 No. 1

No. 2

No. 3

No. 4

Comparative Example 1

The same sintered lead (third sintered lead) as in Example 1 was dippedinto a pigment solution obtained by dissolving 14% by weight of C. I.Pigment Blue 15: 3 (copper phthalocyanine pigment) in 86% by weight of98% sulfuric acid for 24 hours, and then it was dipped into water for 12hours, neutralized, washed with water and rinsed to obtain a light bluesintered pencil lead having a diameter of 0.57 mm.

Comparative Example 2

The same sintered lead (third sintered lead) as in Example 1 was dippedinto a red solution comprising:

Spilon Red C-GH (manufactured by 20% by weight Hodogaya Chemical Co.,Ltd.) Ethyl alcohol 55% by weight Polyoxyethylene lauryl ether 25% byweight

(n=4.5)

and left standing at room temperature for 24 hours. The lead was takenout of the solution and then dried at 80° C. for 5 hours to remove ethylalcohol, whereby a red sintered color pencil lead having a diameter of0.57 mm was obtained.

Measured and evaluated according to the following evaluating methodswere a bending strength, a pore diameter, a light fastness and anerasability of the sintered color pencil leads prepared in Examples 1 to7 and Comparative Examples 1 to 2.

The results thereof are shown in the following Table 2.

(1) Measuring Method for Bending Strength

A bending strength of the lead before and after coloring was measuredbased on JIS-S-6005.

(2) Measuring Method for Pore Diameter

The median pore diameter was measured by means of a mercury porosimeter.

(3) Evaluating Method for Light Fastness

The light fastness was determined by drawing lines on wood free paperand then irradiating them with a xenon lamp for 6 hours to measure adifference (ΔL*) in a lightness index L* of the drawn lines before andafter irradiation. It is shown that the smaller the ΔL* is, the betterthe light fastness.

(4) Evaluating Method for Erasability

The erasability was determined according to the following equation:

erasability (%)=(drawn line density−density after erasing drawnlines)/(drawn line density)×100

The drawn line density was measured based on JIS-S-6005.

TABLE 2 Bending strength MPa Median pore Light Before After diameterErasability fastness coloring coloring μm % ΔL* Example 1 250.5 249.80.18 100.0 0.4 Example 2 250.5 252.1 0.18 99.8 0.3 Example 3 250.5 250.90.18 99.2 0.3 Example 4 250.5 253.0 0.18 100.0 0.3 Example 5 239.7 241.20.15 100.0 0.4 Example 6 209.9 210.1 0.17 99.2 0.3 Example 7 117.0 115.80.23 97.6 0.3 Comparative 250.5 203.4 0.18 100.0 0.6 Example 1Comparative 250.5 249.8 0.18 96.0 12.6 Example 2

Comments on Results Summarized in Table 2

As apparent from the results shown in Table 2 described above, it hasbeen found that the sintered leads prepared in Examples 1 to 7 fallingin the scope of the present invention have a good erasability and areexcellent in light fastness. However, the lead prepared in Example 7 inwhich clay was used as a binder has a bending strength which is not sohigh, and the leads prepared in Examples 1 to 6 have a sufficientlysatisfactory value in terms of practical use.

In contrast with this, it has been found that the sintered lead preparedin Comparative Example 1 is a little reduced in strength because ofdipping in a conc. sulfuric acid solution and that the sintered leadprepared in Comparative Example 2 is inferior in light fastness becausethe colorant was a dye.

Industrial Applicability

According to the present invention, provided is a process for producinga sintered color pencil lead which can draw lines having excellent lightfastness and weatherability while having a vivid coloring property and asufficiently high density in drawn lines and is excellent in amechanical strength such as a bending strength and which can readily beerased with an eraser and is particularly suited as a fine size colorpencil lead for a mechanical pencil.

What is claimed is:
 1. A process for producing a sintered color pencillead characterized by forming a white or light-colored porous sinteredpencil lead that is pigmented with an organic pigment by treating saidporous sintered pencil lead with a solution of at least one compound ofthe following Formula (I) to be filled with said compound and then byforming said organic pigment within the pores by means of heating,A(B)x  (I) in which x is an integer from 1 to 8, A is the radical of achromophore of the quinacridone, anthraquinone, perylene, indigo,quinophthalone, indanthrone, isoindolinone, isoindoline, dioxazine, azoseries, phthalocyanine or diketopyrrolopyrrole which is attached to xgroups B via one or more heteroatoms selected from the group consistingof N, O and S and forming part of the radical A, B is hydrogen or agroup of the formula

where at least one group B is not hydrogen and, if x is 2 to 8, all thegroups B can be identical or different, and L is any suitablesolubilizing group.
 2. The process for producing a sintered color pencillead according to claim 1 in which the compound of Formula (I) isselected from compounds of the following Formulae (IIa) to (XVIb): a)perylencarboximides of the following formulae

in which D is hydrogen, C₁-C₆alkyl, unsubstituted or halo- orC₁-C₆alkyl-substituted phenyl, benzyl or phenethyl or B, where B isidentical to that described above; b) quinacridones of the followingformula (III)

in which R₁ and R₂ independently of one another are hydrogen, halogen,C₁-C₂₄alkyl, C₁-C₆alkoxy or phenyl, and E is hydrogen or a group of thefollowing formula:

in which L is any suitable solubilizing group, with the proviso that atleast one of the groups E is a group other than hydrogen; c) dioxazinesof the following formulae

in which R₃ is hydrogen, halogen or C₁-C₂₄alkyl, and E is identical tothat described above,

in which R₄, R₅ and R₆ independently of one another are hydrogen,C₁-C₄alkyl, C₁-C₄alkoxy, NECOC₁-C₄alkyl, NECOphenyl or N(E)₂, where atleast one of R₄, R₅ and R₆ is NECOC₁-C₄alkyl, NECOphenyl or N(E)₂, and Eis identical to that described above; d) isoindolines of the followingformulae

in which R₇ is a group

R₈ is hydrogen, C₁-C₂₄alkyl, benzyl or a group

R₉ is hydrogen, E or R₇, R₁₀, R₁₁, R₁₂ and R₁₃ independently of oneanother are hydrogen, C₁-C₂₄alkyl, C₁-C₆alkoxy, halogen ortrifluoromethyl, and E is identical to that described above; e)isoindolinones of the following formulae

in which R₁₄ and R₁₅ independently of one another are hydrogen, halogenor C₁-C₄alkyl, and E is identical to that described above; f)anthraquinoid compounds of the following formulae

in which R₁₆'s independently of one another are hydrogen or halogen, andE is identical to that described above; g) phthalocyanines of thefollowing formula

in which M is H₂, a divalent metal selected from the group consisting ofCu (II), Zn (II), Fe (II), Ni (II), Ru (II), Rh (II), Pd (II), Pt (II),Mn (II), Mg (II), Be (II), Ca (II), Ba (II), Cd (II), Hg (II), Sn (II),Co (II) and Pb (II), or a divalent metal oxide selected from the groupconsisting of V(O), Mn(O) and TiO, T₁ is —CHR₁₈—, —CO— or SO₂—, R₁₇ ishydrogen, C₁-C₆alkyl, —N(E)R₁₈, N(E)₂, —NECOR₁₉, —COR₁₉ or a group

R₁₈ is hydrogen or C₁-C₆alkyl, R₁₉ is C₁-C₆alkyl, R₂₀ is hydrogen,halogen, C₁-C₆alkyl or C₁-C₆alkoxy, Z is zero or 1, y is an integer of 1to 8, and E is identical to that described above; h)pyrrolo[3,4-c]pyrroles of the following formulae

in which G₁ and G₂ independently of one another are any of the followinggroups, and E is identical to that described above:

in which R₂₁ and R₂₂ independently of one another are hydrogen, halogen,C₁-C₂₄alkyl, C₁-C₆alkoxy, C₁-C₁₈alkylmercapto, C₁-C₁₈alkylamino, —CN,—NO₂, phenyl, trifluoromethyl, C₅-C₆cycloalkyl, —C═N—(C₁-C₂₄alkyl), agroup

imidazolyl, pyrazolyl, triazolyl, piperadinyl, pyrrolyl, oxazolyl,benzoxazolyl, benzothiazolyl, benzoimidazolyl, morpholinyl, piperidinylor pyrrolidinyl, T₂ is —CH₂—, —CH(CH₃)—, —CH(CH₃)₂—, —CH═N—, —N═N—, —O—,—S—, —SO—, —SO₂— or —NR₂₇, R₂₃ and R₂₄ independently of one another arehydrogen, halogen, C₁-C₆alkyl, C₁-C₆alkoxy or —CN, R₂₅ and R₂₆independently of one another are hydrogen, halogen or C₁-C₆alkyl, R₂₇ ishydrogen or C₁-C₆alkyl: i) quinophthalones of the following formulae

in which R₂₈ is hydrogen or O—E, R₂₉, R₃₀, R₃₁ and R₃₂ independently ofone another are hydrogen, halogen, —COO—C₁-C₆alkyl or —CONE—C₁-C₆alkyl,and E is identical to that described above; j) azo compounds of thefollowing formulae

in which R₃₃, R₃₄, R₃₅, R₃₆ and R₃₇ independently of one another arehydrogen, halogen, C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, acetyl or—SO₂NE—C₁-C₆alkyl, R₃₈ is hydrogen, halogen, C₁-C₆alkyl or C₁-C₆alkoxy;and E is identical to that described above; k) anthraquinones of thefollowing formulae

in which R₃₉ and R₄₀ independently of one another are hydrogen,C₁-C₁₂alkyl or C₆-C₁₂aryl which is unsubstituted or substituted byhalogen, C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, acetyl, SO₂NE—C₁-C₆alkyl or—SO₂NE₂, R₄₁ and R₄₂ independently of one another are hydrogen, halogen,C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, cyano, CONE₂, SO₂NEC₁-C₆alkyl or SO₂NE₂,SO₃E, SO₃Na or C₆-C₁₂aryl which is unsubstituted or substituted byhalogen, C₁-C₆alkyl, C₁-C₆alkoxy, NO₂, acetyl, SO₂NEC₁-C₆alkyl orSO₂NE₂, R₄₃ is hydrogen, halogen, NO₂, cyano, hydroxyl or C₁-C₆alkoxy;and B and E are identical to that described above; and l) indigoderivatives of the following formula

in which R₄₄ is hydrogen, halogen, cyano, C₁-C₆alkyl or C₁-C₆alkoxy, andE is identical to that described above.
 3. The process for producing asintered color pencil lead according to claim 2 in which the —L group inthe B group in Formula (I) is any one of the following formulae

in which R₅₀, R₅₁ and R₅₂ independently of one another are C₁-C₆alkyl,R₅₃ and R₅₄ independently of one another are C₁-C₆alkyl, oxygen-,sulfur- or N(R₆₁)₂-interrupted C₁-C₆alkyl, unsubstituted or halo-,C₁-C₆alkyl-, C₁-C₆alkoxy-, NO₂— or cyano-substituted phenyl orbiphenylyl, R₅₅, R₅₆ and R₅₇ independently of one another are hydrogenor C₁-C₆alkyl, R₅₈ is hydrogen, C₁-C₆alkyl or any of the followinggroups:

R₅₉ and R₆₀ independently of one another are hydrogen, halogen,C₁-C₆alkyl, C₁-C₆alkoxy, cyano, NO₂, N(R₆₁)₂, unsubstituted or halo-,C₁-C₆alkyl-, C₁-C₆alkoxy-, NO₂— or cyano-substituted phenyl, R₆₁ and R₆₂are C₁-C₆alkyl, R₆₃ is hydrogen or C₁-C₆alkyl, R₆₄ is hydrogen,C₁-C₆alkyl, unsubstituted or C₁-C₆alkyl-substituted phenyl, Q isp,q-C₂-C₆alkylene which is unsubstituted or substituted once or moretimes by C₁-C₆alkoxy, C₁-C₆alkylmercapto or C₂-C₁₂dialkylamino (where pand q are different numeric locants), X is a heteroatom selected fromthe group consisting of N, O and S, where m is 0 if X is O or S and is 1if X is N, L₁ and L₂ independently of one another are unsubutituted ormono- or poly-C₁-C₁₂alkoxy, —C₁-C₁₂alkylmercapto, —C₂-C₂₄dialkylamino,—C₆-C₁₂aryloxy, —C₆-C₁₂arylmercapto, —C₇-C₂₄alkylarylamino or—C₁₂-C₂₄diarylamino-substituted C₁-C₆alkyl, or[-(p′,q′-C₂-C₆alkylene)-Z—]_(n)—C₁-C₆alkyl (where n is a number of 1 to1000; p′ and q′ are different numeric locants; each Z independently ofthe others is a heteroatom comprising oxygen, sulfur orC₁-C₁₂alkyl-substituted nitrogen; and all C₂-C₆alkylenes in therepeating units [—C₂-C₆alkylene-Z—] can be identical or different), L₁and L₂ can be saturated or mono- to deca-unsaturated, uninterrupted orinterrupted in any desired points by from 1 to 10 groups selected fromthe group consisting of —(C═O)— and —C₆H₄—, and may carry no or 1 to 10further substituents selected from the group consisting of halogen,cyano and NO₂.
 4. The process for producing a sintered color pencil leadaccording to claim 3 in which the white or light-colored porous sinteredlead comprises a colorless or white filler and silicon nitride preparedfrom a starting material of perhydropolysilazane that is a binder. 5.The process for producing a sintered color pencil lead according toclaim 1 in which the —L group in the B group in Formula (I) is any oneof the following formulae

in which R₅₀, R₅₁ and R₅₂ independently of one another are C₁-C₆alkyl,R₅₃ and R₅₄ independently of one another are C₁-C₆alkyl, oxygen-,sulfur- or N(R₆₁)₂-interrupted C₁-C₆alkyl, unsubstituted or halo-,C₁-C₆alkyl-, C₁-C₆alkoxy-, NO₂— or cyano-substituted phenyl orbiphenylyl, R₅₅, R₅₆ and R₅₇ independently of one another are hydrogenor C₁-C₆alkyl, R₅₈ is hydrogen, C₁-C₆alkyl or any of the followinggroups:

R₅₉ and R₆₀ independently of one another are hydrogen, halogen,C₁-C₆alkyl, C₁-C₆alkoxy, cyano, NO₂, N(R₆₁)₂, unsubstituted or halo-,C₁-C₆alkyl-, C₁-C₆alkoxy-, NO₂— or cyano-substituted phenyl, R₆₁ and R₆₂are C₁-C₆alkyl, R₆₃ is hydrogen or C₁-C₆alkyl, R₆₄ is hydrogen,C₁-C₆alkyl, unsubstituted or C₁-C₆alkyl-substituted phenyl, Q isp,q-C₂-C₆alkylene which is unsubstituted or substituted once or moretimes by C₁-C₆alkoxy, C₁-C₆alkylmercapto or C₂-C₁₂dialkylamino (where pand q are different numeric locants), X is a heteroatom selected fromthe group consisting of N, O and S, where m is 0 if X is O or S and is 1if X is N, L₁ and L₂ independently of one another are unsubutituted ormono- or poly-C₁-C₁₂alkoxy, —C₁-C₁₂alkylmercapto, —C₂-C₂₄dialkylamino,—C₆-C₁₂aryloxy, —C₆-C₁₂arylmercapto, —C₇-C₂₄alkylarylamino or—C₁₂-C₂₄diarylamino-substituted C₁-C₆alkyl, or[-(p′,q′-C₂-C₆alkylene)-Z—]_(n)—C₁-C₆alkyl (where n is a number of 1 to1000; p′ and q′ are different numeric locants; each Z independently ofthe others is a heteroatom comprising oxygen, sulfur orC₁-C₁₂alkyl-substituted nitrogen; and all C₂-C₆alkylenes in therepeating units [—C₂-C₆alkylene-Z—] can be identical or different), L₁and L₂ can be saturated or mono- to deca-unsaturated, uninterrupted orinterrupted in any desired points by from 1 to 10 groups selected fromthe group consisting of —(C═O)— and —C₆H₄—, and may carry no or 1 to 10further substituents selected from the group consisting of halogen,cyano and NO₂.
 6. The process for producing a sintered color pencil leadaccording to claim 5 in which the white or light-colored porous sinteredlead comprises a colorless or white filler and silicon nitride preparedfrom a starting material of perhydropolysilazane that is a binder. 7.The process for producing a sintered color pencil lead according toclaim 2 in which the white or light-colored porous sintered leadcomprises a colorless or white filler and silicon nitride prepared froma starting material of perhydropolysilazane that is a binder.
 8. Theprocess for producing a sintered color pencil lead according to claim 1in which the white or light-colored porous sintered lead comprises acolorless or white filler and silicon nitride prepared from a startingmaterial of perhydropolysilazane that is a binder.